Drought is one of the major limiting factors for plant productivity and spatial distribution. The annual loss in yield of major cereal crops due to drought is estimated to exceed ten billion dollars globally. Desertification, defined as “Land degradation in arid, semi-arid and dry sub-humid areas,” is happening in about 70% of the total of the world's dry lands (3.6 billion hectares) and has become a very distinctive global issue with major environmental consequences. It affects about 25% of the total land area of the world and about 17% of the world population. Conventional crop improvement for enhanced drought tolerance has been ineffective, mainly due to limited germplasm resources and incompatibility in crosses between distantly related plant species.
Development of drought-tolerant plant species through biotechnology is both economically and environmentally important. Recent advances in plant gene discovery and genetic transformation have begun provide the tools for generating stress-tolerant crops using transgenic approaches. Despite the enormous economic and environmental significance, development of transgenic crops that confer drought tolerance in a highly controlled manner remains a challenge.